A 13-year-old boy has been charged over a series of alleged sexual offences against females on popular walking trails in Sydney’s Northern Beaches.

Police allege 11 separate incidents involving females aged between 13 and 54 occurred in the Narrabeen area between October 1 and October 12.

WATCH THE VIDEO ABOVE: Teen charged over Narrabeen Lagoon Trail assaults

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Detectives from Northern Beaches Police Area Command established Strike Force Mexvo to investigate the reports of alleged sexual touching and inappropriate comments made towards females on the walking trails.

Police initially began investigating after three alleged incidents in two days, in which a male allegedly sexually touched women on walking trails before fleeing on an e-bike.

Further reports followed, including two women who alleged they were sexually touched by a male riding an e-bike near Bilarong Reserve on October 12.

Police initially began investigating after three alleged incidents in two days. Credit: Sunrise/NSW Police

The alleged incidents occurred in broad daylight, mostly between 4pm and 6pm, around Narrabeen Lagoon and surrounding walking trails.

Police increased patrols in the area, deploying uniformed and plain-clothes officers as part of the investigation.

Investigators are also probing an alleged incident in which a woman was spoken to inappropriately at the intersection of Waroon Road and Carawa Road in Cromer about 6.45pm on September 7.

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Following a public appeal, the 13-year-old boy presented himself to Mona Vale Police Station about 7.30pm on Saturday, October 17, where he was arrested.

He was taken to Manly Police Station and charged with three counts of behaving in an offensive manner in or near a public place or school, and eight counts of sexually touching another person without consent.

The boy was granted conditional bail and is due to appear before a children’s court on Wednesday, November 4.

If you or someone you know needs help, contact 1800 RESPECT (1800 737 732), or Sexual Assault Counselling Australia on 1800 211 028, the WA Sexual Assault Resource Centre on 6458 1828 or 1800 199 888 or Lifeline on 13 11 14.